U.S. patent number 6,970,644 [Application Number 09/747,522] was granted by the patent office on 2005-11-29 for heating configuration for use in thermal processing chambers.
This patent grant is currently assigned to Mattson Technology, Inc.. Invention is credited to Rudy Santo Tomas Cardema, Shuen Chun Choy, Zion Koren, Conor Patrick O'Carroll, Arieh A. Strod, James Tsuneo Taoka, Paul Janis Timans.
United States Patent |
6,970,644 |
Koren , et al. |
November 29, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Heating configuration for use in thermal processing chambers
Abstract
An apparatus for heat treating semiconductor wafers is
disclosed. The apparatus includes a heating device which contains
an assembly linear lamps for emitting light energy onto a wafer.
The linear lamps can be placed in various configurations. In
accordance with the present invention, tuning devices which are
used to adjust the overall irradiance distribution of the light
energy sources are included in the heating device. The tuning
devices can be, for instance, are lamps or lasers.
Inventors: |
Koren; Zion (Sunnyvale, CA),
O'Carroll; Conor Patrick (Sunnyvale, CA), Choy; Shuen
Chun (San Francisco, CA), Timans; Paul Janis (Mountain
View, CA), Cardema; Rudy Santo Tomas (San Jose, CA),
Taoka; James Tsuneo (San Jose, CA), Strod; Arieh A.
(Cupertino, CA) |
Assignee: |
Mattson Technology, Inc.
(Fremont, CA)
|
Family
ID: |
25005424 |
Appl.
No.: |
09/747,522 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
392/418; 118/724;
118/725; 219/121.6; 219/121.82; 219/390; 219/405; 219/411; 392/416;
428/428; 501/50; 501/64 |
Current CPC
Class: |
C23C
16/481 (20130101); C30B 25/105 (20130101); C30B
31/12 (20130101); H01L 21/67115 (20130101) |
Current International
Class: |
F26B 003/30 () |
Field of
Search: |
;219/390,405,411,121.6-121.66,121.74-121.78,121.82 ;392/416,418
;118/724,725,501 ;501/50,64 ;428/428 |
References Cited
[Referenced By]
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Other References
Luk'yanchuck. Sov. J. Quantum Electro. 9(10), Oct. 1979. .
Article--Temperature measurement in rapid thermal processing, Paul
J. Timans, Solid State Technology, Apr. 1997, 6 pages. .
Article--Reduced Thermal Processing for ULSI, C. Hill, S. Jones,
and D. Boys, Rapid Thermal Annealing--Theory and Practice, pp.
143-180. .
Article--Application of Rapid Thermal Processing in Manufacturing:
The Effect of Emissivity and Coupling, James S. Nakos, pp. 421-428.
.
Article--The Effect of Multilayer Patterns on Temperature
Uniformity during Rapid Thermal Processing, Jeffrey P. Hebb and
Klavs F. Jensen, J. Electrochem. Soc., vol. 143, No. 3, Mar. 1996,
pp. 1142-1151. .
Article--Beam Processing In Silicon Device Technology, C. Hill,
Laser and Electron-Beam Solid Interactions and Materials Process,
1981, pp. 361-374. .
Article--Absorption of Infrared Radiation in Silicon, I.W. Boyd,
T.D. Binnie, J.I.B. Wilson, and M. J. Colles, J. Appl. Phys. 55
(8), Apr. 15, 1984, pp. 3061-3063..
|
Primary Examiner: Fuqua; Shawntina
Attorney, Agent or Firm: Dority & Manning, P.A.
Claims
What is claimed is:
1. An apparatus for heat treating semiconductor wafers comprising:
a thermal processing chamber adapted to contain a semiconductor
wafer; and a heating device in communication with said thermal
processing chamber for heating a semiconductor wafer contained in
said chamber, said heating device comprising: (a) a plurality of
light energy sources configured to emit light energy onto said
semiconductor wafer, said light energy sources comprising linear
lamps horizontally oriented with respect to said wafer, said light
energy sources being positioned so as to form an irradiance
distributior across a surface of said wafer; and (b) at least one
tuning device positioned amongst said light energy sources, the
tuning device comprising a plurality of lasers, said lasers
emitting light energy at more than one wavelength.
2. An apparatus as defined in claim 1, wherein said tuning device
further comprises at least one focusing lens, said focusing lens
being configured to focus light energy being emitted by said tuning
device.
3. An apparatus as defined in claim 1, further comprising a light
pipe positioned in operative association with said tuning device
for directing light energy being emitted by said tuning device onto
said semiconductor wafer.
4. An apparatus as defined in claim 1, wherein said tuning device
is positioned to heat the outer edges of said wafer.
5. An apparatus as defined in claim 1, further comprising: at least
one temperature sensing device for sensing the temperature of said
semiconductor wafer at least at one location; and a controller in
communication with said at least one temperature sensing device and
at least certain of said light energy sources, said controller
being configured to control the amount of light energy being
emitted by said light energy sources in response to temperature
information received from said at least one temperature sensing
device.
6. An apparatus as defined in claim 1, further comprising a
substrate holder for holding said semiconductor wafer, said
substrate holder being configured to rotate said wafer.
7. An apparatus as defined in claim 1, wherein at least one laser
emits p-polarized light.
8. An apparatus as defined in claim 7, wherein said laser emits
light energy having an angle of incidence relative to said
semiconductor wafer of about 40.degree. to about 85.degree..
9. An apparatus for heat treating semiconductor wafers comprising:
a thermal processing chamber adapted to contain a semiconductor
wafer; a substrate holder positioned within said thermal processing
chamber, said substrate holder being configured to hold said
semiconductor wafer and rotate said wafer in said chamber; and a
heating device in communication with said thermal processing
chamber for heating a semiconductor wafer contained in said
chamber, said heating device comprising: (a) a plurality of linear
lamps configured to emit light energy onto said semiconductor
wafer, said linear lamps being horizontally oriented with respect
to said wafer and extending from one side of said thermal
processing chamber to an opposite side, said linear lamps being
positioned so as to form an irradiance distribution across the
surface of said wafer; (b) a plurality of tuning devices, said
tuning devices being configured to emit focused light energy onto
particular locations of said wafer, at least certain of said tuning
devices being positioned to heat the outer most edges of said
semiconductor wafer and wherein the tuning devices comprise lasers,
said lasers emitting light energy at more than one wavelength.
10. An apparatus as defined in claim 9, further comprising: at
least one temperature sensing device for sensing the temperature of
said semiconductor wafer at least at one location; and a controller
in communication with said temperature sensing device, with at
least certain of said linear lamps, and with said tuning devices,
said controller being configured to control the amount of light
energy being emitted by said linear lamps and said tuning devices
in response to temperature information received from said
temperature sensing device.
11. An apparatus as defined in claim 10, wherein said controller is
configured to control the amount of light energy being emitted by
said tuning devices independently of said linear lamps.
12. An apparatus as defined in claim 10, wherein at least one of
the lasers emit p-polarized light.
13. An apparatus as defined in claim 10, wherein said lasers emit
light onto said wafer at an angle of incidence of from about
40.degree. to about 85.degree..
14. An apparatus for heat treating semiconductor wafers comprising:
a thermal processing chamber adapted to contain a semiconductor
wafer; a substrate holder positioned within the thermal processing
chamber, the substrate holder being configured to hold the
semiconductor wafer in the chamber; a first heating device in
communication with the thermal processing chamber for heating a
semiconductor wafer contained in the chamber; and a second heating
device comprising a plurality of tuning devices that emit light
energy onto the semiconductor wafer, the tuning devices comprising
lasers, the lasers emitting light energy at more than one
wavelength.
15. An apparatus as defined in claim 14, wherein at least one of
the lasers is in communication with a focusing lens, the focusing
lens being configured to focus light energy being emitted by the at
least one laser.
16. An apparatus as defined in claim 14, wherein at least one of
the lasers is positioned to emit light energy onto the outer edged
of the wafer.
17. An apparatus as defined in claim 14, further comprising: at
least one temperature sensing device for sensing the temperature of
the semiconductor wafer; and a controller in communication with the
at least one temperature sensing device and the first heating
device, the controller being configured to control the amount of
energy being emitted by the first heating device in response to
temperature information received from the at least one temperature
sensing device.
18. An apparatus as defined in claim 14, wherein the substrate
holder is configured to rotate the wafer.
19. An apparatus as defined in claim 14, wherein at least one of
the lasers emits p-polarized light.
20. An apparatus as defined in claim 14, wherein at least one of
the lasers emits light energy having an angle of incidence relative
to the semiconductor wafer of about 40.degree. to about
85.degree..
21. An apparatus as defined in claim 19, wherein at least one of
the lasers emits light energy having an angle of incidence relative
to the semiconductor wafer of about 40.degree. to about
85.degree..
22. An apparatus as defined in claim 17, wherein the controller is
also configured to control the second heating device independently
of the first heating device.
23. An apparatus as defined in claim 14, wherein each of the lasers
emits light onto the wafer at an angle of incidence of from about
40.degree. to about 85.degree..
24. An apparatus as defined in claim 1, wherein the tuning device
is moved in relation to the semiconductor wafer in order to change
the location of where the light energy being emitted by the tuning
device contacts the wafer.
25. An apparatus as defined in claim 9, wherein the plurality of
tuning devices are movable in relation to the wafer in order to
change the location of where the light energy being emitted by the
tuning devices contacts the wafer.
26. An apparatus as defined in claim 14, wherein the plurality of
tuning devices are movable in relation to the semiconductor wafer
in order to change the location of where the light energy being
emitted by the second heating device contacts the wafer.
27. An apparatus as defined in claim 14, further comprising: at
least one temperature sensing device for sensing the temperature of
semiconductor wafer; and a controller in communication with the at
least one temperature sensing device and the first heating device,
the controller being configured to control the amount of energy
being emitted by the second heating device in response to
temperature information received from the at least one temperature
sensing device.
28. An apparatus as defined in claim 1, wherein said laser emits
light energy having an angle of incidence relative to said
semiconductor wafer of about 40.degree. to about 85.degree..
29. An apparatus as defined in claim 12, wherein said lasers emit
light onto said wafer at an angle of incidence of from about
40.degree. to about 85.degree..
Description
BACKGROUND OF THE INVENTION
A thermal processing chamber as used herein refers to a device that
rapidly heats objects, such as semiconductor wafers. Such devices
typically include a substrate holder for holding a semiconductor
wafer and a light source that emits light energy for heating the
wafer. During heat treatment, the semiconductor wafers are heated
under controlled conditions according to a preset temperature
regime. For monitoring the temperature of the semiconductor wafer
during heat treatment, thermal processing chambers also typically
include temperature sensing devices, such as pyrometers, that sense
the radiation being emitted by the semiconductor wafer at a
selected band of wavelengths. By sensing the thermal radiation
being emitted by the wafer, the temperature of the wafer can be
calculated with reasonable accuracy.
In alternative embodiments, instead of or in addition to using
radiation sensing devices, thermal processing chambers can also
contain thermocouples for monitoring the temperature of the wafers.
Thermocouples measure the temperature of objects by direct
contact.
Many semiconductor heating processes require a wafer to be heated
to high temperatures so that various chemical and physical
reactions can take place as the wafer is fabricated into a device.
During rapid thermal processing, which is one type of processing,
semiconductor wafers are typically heated by an array of lights to
temperatures, for instance, from about 400.degree. C. to about
1,200.degree. C., for times which are typically less than a few
minutes. During these processes, one main goal is to heat the
wafers as uniformly as possible.
Problems have been experienced in the past, however, in being able
to maintain a constant temperature throughout the wafer and in
being able to control the rate at which the wafer is heated. If the
wafer is heated nonuniformly, various unwanted stresses can develop
in the wafer. Not being able to heat the wafers uniformly also
limits the ability to uniformly deposit films on the wafers, to
uniformly etch the wafers, beside limiting the ability to perform
various other chemical and physical processes on the wafers.
Temperature gradients can be created within the wafer due to
various factors. For instance, due to the increased surface area to
volume ratio, the edges of semiconductor wafers tend to have a
cooling rate and a heating rate that are different than the center
of the wafer. The energy absorption characteristics of wafers can
also vary from location to location. Additionally, when gases are
circulated in the chamber, the gases can create cooler areas on the
wafer due to convection.
In the past, various lamp configurations have been proposed in
order to overcome the above described deficiencies and improve the
ability to heat wafers more uniformly and to control the
temperature of the wafers at various locations. These systems,
however, have become increasingly complex and expensive to produce.
For instance, some systems can contain well over 100 lamps.
As such, a need currently exists for an improved thermal processing
chamber that is capable of uniformly heating semiconductor wafers
in a relatively simple manner without being as complex as many
prior art systems. A need also exists for an improved rapid thermal
processing chamber for heating semiconductor wafers that is
equipped with controls for varying the amount of energy that is
applied to the wafer at different locations based upon the
characteristics and properties of the wafer. Such controls are
especially necessary due to the increasing demands that are being
placed upon the preciseness at which the semiconductor wafers are
heat treated and at which semiconductor devices are fabricated.
SUMMARY OF THE INVENTION
The present invention is generally directed to an apparatus for
heat treating semiconductor wafers. The apparatus includes a
thermal processing chamber adapted to contain a semiconductor
wafer. For instance, a substrate holder can be contained within the
chamber upon which the wafer is held. A heating device is placed in
communication with the thermal processing chamber which emits
thermal light energy onto the wafer held on the substrate holder.
The heating device can include an assembly of light energy sources
which are positioned, for instance, to heat different zones of the
wafer. The light energy sources form an irradiance distribution
across a surface of the wafer.
In particular, the light energy sources used in the present
invention are linear lamps positioned above the wafer, below the
wafer, or above and below the wafer. Linear lamps are elongated
lamps that are typically oriented horizontally with respect to the
wafer being heated. Although the lamps can be any shape, such as
circular, for most applications, the lamps have a long rod-like
shape that extend the length of the wafer being heated, such as
from one end of the thermal processing chamber to the other. For
example, a series of rod-like lamps positioned parallel to each
other, can be located over the wafer.
During the heating process, the semiconductor wafer can be rotated.
In this manner, the light energy sources form radial heating zones
on the wafer which aid in heating the wafer uniformly and provide
good temporal control during the heating cycle.
In accordance with the present invention, the heating device
further includes at least one tuning device positioned amongst the
linear lamps. The tuning device is configured to change the
irradiance distribution of the linear lamps in a manner for more
uniformly heating the semiconductor wafer.
The tuning devices proved localized temperature control on the
wafer. Through the combination of linear lamps and tuning sources,
the present invention allows the processing system to achieve a
better temperature uniformity across the wafer or a better
realization of a desired temperature profile. In one embodiment,
the system can also be used to radially fine tune the whole wafer
for further improving temperature uniformity.
The tuning device used in the present invention can be any suitable
lamp or lamp configuration that is capable of directing a focused
light beam onto a certain location of a substrate. For instance, in
one embodiment, the tuning device can be a laser. The laser can
emit p-polarized light onto the wafer. In order to maximize
absorption, the laser can be adjusted so that the angle of
incidence corresponds to where reflectivity of the light at the
particular wavelength is at a minimum. For example, when processing
silicon wafers, the angle of incidence can be generally less than
90.degree., and particularly from about 40.degree. to about
85.degree..
Further, since most lasers emit light at a particular wavelength,
in an alternative embodiment of the present invention, multiple
lasers can be used that emit light at different wavelengths. By
using different types of lasers, problems associated with
reflectivity can be minimized.
Besides lasers, arc lamps can also be used as the tuning device.
Arc lamps are well suited to emitting light that can be focused
onto a particular portion of the wafer. When used in the system of
the present invention, an arc lamp can be coupled to a light pipe
and at least one focusing lens for directing light being emitted by
the arc lamp onto a particular location.
The system of the present invention can include as many tuning
devices as are required for uniformly heating wafers. The number of
tuning devices incorporated into a particularly system will
generally depend upon numerous factors, including the configuration
of the light energy sources.
In order to control the amount of light energy that is emitted by
the plurality of light energy sources, the apparatus of the present
invention can include at least one temperature sensing device which
senses the temperature of the wafer at a plurality of locations.
For instance, the temperature sensing device can be a plurality of
pyrometers, one pyrometer with multiple viewing ports, or one or
more thermocouples. The temperature sensing devices can be in
communication with a controller, such as a microprocessor, which
determines the temperature of the wafer. The controller, in turn,
can be in communication with the power supply of the linear lamps
for controlling the amount of heat being emitted by the light
energy sources in response to the temperature of the wafer. The
controller can be configured, for instance, to control the amount
of light energy being emitted by each linear lamp or can control
different groups of the light energy sources.
In one embodiment, the controller can be configured to also control
the amount of light energy that is being emitted by a tuning device
installed in accordance with the present invention. In particular,
the controller can be used to control the tuning device independent
of the linear lamps. Further, the controller can also be configured
to be capable of automatically moving the support structure upon
which the tuning device is mounted in order to change and adjust
the location of where the light energy being emitted by the tuning
device contacts the wafer.
Other features and aspects of the present invention are discussed
in greater detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
A full and enabling disclosure of the present invention, including
the best mode thereof, directed to one of ordinary skill in the
art, is set forth more particularly in the remainder of the
specification, which makes reference to the appended figures in
which:
FIG. 1 is a cross-sectional view of one embodiment of a thermal
processing chamber that may be used in accordance with the present
invention;
FIG. 2 is a cross-sectional perspective view of one embodiment of a
heating device that may be used in thermal processing chambers made
in accordance with the present invention;
FIG. 3 is a cross-sectional perspective view of the heating device
illustrated in FIG. 2;
FIG. 4 is a perspective view of the heating device illustrated in
FIG. 2;
FIG. 5 is a bottom view of the heating device illustrated in FIG.
2; and
FIG. 6 is a side view of one embodiment of a tuning device made in
accordance with the present invention.
Repeat use of references characters in the present specification
and drawings is intended to represent same or analogous features or
elements of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It is to be understood by one of ordinary skill in the art that the
present discussion is a description of exemplary embodiments only,
and is not intended as limiting the broader aspects of the present
invention, which broader aspects are embodied in the exemplary
construction.
A rapid thermal processing apparatus uses intense light to heat a
semiconductor wafer as part of the manufacturing process of
integrated circuits. Exposure to light energy causes a rapid
increase in the temperature of a semiconductor wafer and allows
processing times to be relatively short. In rapid thermal
processing systems, it is important to radiate the wafer with very
high intensity light in a very uniform and controlled fashion. As
stated above, the difficulty with current devices is that the
requirements for the intensity of the radiated light and the
ability to heat wafers uniformly are very difficult to achieve.
In general, the present invention is directed to an apparatus and
method for heating semiconductor wafers uniformly and at a
controlled rate. The apparatus includes a thermal processing
chamber in communication with a heating device that is used to heat
treat semiconductor wafers contained in the chamber. The heating
device contains a plurality of lamps that are positioned at
preselected locations for heating the wafers. The lamps emit light
energy and form a irradiance distribution over the surface of the
wafer.
The heating device and processing chamber of the present invention
are particularly designed to operate with linear lamps. As used
herein, a "linear lamp" refers to a lamp that is designed to emit
most of its energy through the longest dimension of the lamp. For
instance, in most embodiments, linear lamps emit the majority of
their energy through the side of the lamp. Thus, when heating
semiconductor wafers, the lamps are typically horizontally oriented
over and/or below the wafers.
Recently, as opposed to using linear lamps, many thermal processing
chambers have been made with vertically oriented lamps. These lamps
are designed to emit energy out of an end of the lamp for heating
the wafers. The present inventors have discovered that using linear
lamps provide various advantages over vertical lamps. For instance,
when using linear lamps, a much smaller number of lamps are
required to be incorporated into the heating device, since a linear
lamp can heat a much larger area than a vertical lamp. Because less
lamps are required, the system generally becomes more reliable and
easier to maintain. Further, the linear lamps provide good heating
uniformity and make it much easier to heat a wafer from both sides
of the wafer.
During heating, the wafer is rotated with respect to the plurality
of lamps. In this manner, the lamps form radial heating zones on
the wafer. The energy supplied to each heating zone can be
controlled while the wafer is being heated.
In one embodiment, the temperature at different locations of the
wafer is monitored. Based upon the temperature sensed at the
different locations, the energy being emitted by the lamps is
selectively controlled.
In accordance with the present invention, the heating device in
communication with the thermal processing chamber further contains
tuning devices which are designed to modify the irradiance
distribution of the heating lamps for more uniformly heating the
semiconductor wafer. The tuning devices allow fine adjustments to
be made to the wafer irradiance distribution pattern in order to
heat the wafer under a more controlled temperature regime and more
uniformly. The tuning device can be, in one embodiment, a localized
and focused source of light energy that can be directed onto a
particular location on the wafer.
The tunning device can be an active localized source such as a
tungsten halogen bulb in an optical configuration, an arc lamp, or
a laser diode with relatively high power.
Referring to FIG. 1, a system generally 10 made in accordance with
the present invention for heat treating a wafer made from a
semiconductive material, such as silicon, is illustrated. System 10
includes a processing chamber 12 adapted to receive substrates such
as a wafer 14 for conducting various processes. As shown, wafer 14
is positioned on a substrate holder 15 made from a thermal
insulating material such as quartz. Chamber 12 is designed to heat
wafer 14 at very rapid rates and under carefully controlled
conditions. Chamber 12 can be made from various materials,
including metals and ceramics. For instance, chamber 12 can be made
from stainless steel or quartz.
When chamber 12 is made from a heat conductive material, preferably
the chamber includes a cooling system. For instance, as shown in
FIG. 1, chamber 12 includes a cooling conduit 16 wrapped around the
perimeter of the chamber. Conduit 16 is adapted to circulate a
cooling fluid, such as water, which is used to maintain the walls
of chamber 12 at a constant temperature.
Chamber 12 can also include a gas inlet 18 and a gas outlet 20 for
introducing a gas into the chamber and/or for maintaining the
chamber within a preset pressure range. For instance, a gas can be
introduced into chamber 12 through gas inlet 18 for reaction with
wafer 14. Once processed, the gas can then be evacuated from the
chamber using gas outlet 20.
Alternatively, an inert gas can be fed to chamber 12 through gas
inlet 18 for preventing any unwanted or undesirable side reactions
from occurring within the chamber. In a further embodiment, gas
inlet 18 and gas outlet 20 can be used to pressurize chamber 12. A
vacuum can also be created in chamber 12 when desired, using gas
outlet 20 or an additional larger outlet positioned beneath the
level of the wafer.
During processing, substrate holder 15, in one embodiment, can be
adapted to rotate wafer 14 using a wafer rotation mechanism 21.
Rotating the wafer promotes greater temperature uniformity over the
surface of the wafer and promotes enhanced contact between wafer 14
and any gases introduced into the chamber. It should be understood,
however, that besides wafers, chamber 12 is also adapted to process
optical parts, films, fibers, ribbons, and other substrates having
any particular shape.
A heat source or heating device generally 22 is included in
communication with chamber 12 for heating wafer 14 during
processing. Heating device 22 includes a plurality of linear lamps
24, such as tungsten-halogen lamps. As shown in FIG. 1, lamps 24
are horizontally aligned above wafer 14. It should be understood,
however, that lamps 24 may be placed at any particular location
such as only below the wafer or above and below the wafer. Further,
additional lamps could be included within system 10 if desired.
The use of linear lamps 24 as a heat source is generally preferred.
For instance, lamps have much higher heating and cooling rates than
other heating devices, such as electrical elements or conventional
furnaces. Lamps 24 create a rapid isothermal processing system that
provide instantaneous energy, typically requiring a very short and
well controlled start up period. The flow of energy from lamps 24
can also be abruptly stopped at any time. As shown in the figure,
lamps 24 are equipped with a gradual power controller 25 that can
be used to increase or decrease the light energy being emitted by
any of the lamps.
In order to assist in directing the light energy being emitted by
lamps 24 onto wafer 14, the lamps can be associated with a
reflector or a set of reflectors. For instance, as shown in FIG. 1,
the heating device 22 includes a reflector plate 36 positioned
above the linear lamps 24. Reflector plate 36 can be made from any
material suitable for reflecting light energy and can have any
suitable shape that will assist in directing the light energy
toward the wafer 14.
In order to monitor the temperature of wafer 14 during the heating
process, in this embodiment, thermal processing chamber 12 includes
plurality of radiation sensing devices generally 27. Radiation
sensing devices 27 include a plurality of optical fibers or light
pipes 28 which are, in turn, in communication with a plurality of
corresponding light detectors 30. Optical fibers 28 are configured
to receive thermal energy being emitted by wafer 14 at a particular
wavelength. The amount of sensed radiation is then communicated to
light detectors 30 which generate a usable voltage signal for
determining the temperature of the wafer which can be calculated
based, in part, on Planck's Law. In one embodiment, each optical
fiber 28 in combination with a light detector 30 comprises a
pyrometer. In another embodiment, the optical fibers 28 are routed
to a single but multiplexing radiation sensing device.
In general, thermal processing chamber 12 can contain one or a
plurality of radiation sensing devices. In a preferred embodiment,
as shown in FIG. 1, thermal processing chamber 12 contains a
plurality of radiation sensing devices that measure the temperature
of the wafer at different locations. Knowing the temperature of the
wafer at different locations can then be used to control the amount
of heat being applied to the wafer as will be described in more
detail hereinafter. The amount of heat applied to various zones of
the wafer can also be controlled in an open loop fashion. In this
configuration the ratios between the various heating zones can be
pre-determined after manual optimization.
System 10 further includes a window 32 which separates lamps 24
from the chamber. Window 32 serves to isolate lamps 24 from wafer
14 and prevent contamination of the chamber. Window 32 as shown in
FIG. 1 can be a window positioned between chamber 12 and heat
source 22. In an alternative embodiment, each lamp 24 can be
covered by a separate window casing.
Besides using radiation sensing devices, other temperature sensing
devices may be used in the system of the present invention. For
instance, one or more thermocouples may be incorporated into the
system for monitoring the temperature of the wafer at a single
location or at a plurality of locations. The thermocouples can be
placed in direct contact with the wafer or can be placed adjacent
the wafer from which the temperature can be extrapolated.
System 10 further includes a system controller 50 which can be, for
instance, a microprocessor. Controller 50 receives voltage signals
from light detectors 30 that represent the radiation amounts being
sampled at the various locations. Based on the signals received,
controller 50 is configured to calculate the temperature of wafer
14 at different locations.
System controller 50 as shown in FIG. 1 can also be in
communication with lamp power controller 25. In this arrangement,
controller 50 can determine the temperature of wafer 14, and, based
on this information, control the amount of thermal energy being
emitted by lamps 24. In this manner, instantaneous adjustments can
be made regarding the conditions within reactor 12 for processing
wafer 14 within carefully controlled limits.
In one embodiment, controller 50 can also be used to automatically
control other elements within the system. For instance, controller
50 can be used to control the flow rate of gases entering chamber
12 through gas inlet 18. As shown, controller 50 can further be
used to control the rate at which wafer 14 is rotated within the
chamber.
As described above, the present invention is generally directed to
a particular heating configuration that is used within thermal
processing chamber 12. Referring to FIGS. 2 through 5, one
embodiment of a heating device 22 that can be used in combination
with thermal processing chamber 12 in accordance with the present
invention is illustrated. As shown, heating device 22 includes a
plurality of light energy sources, such as linear lamps 24 that are
secured to a mounting base 34. The linear lamps 24 each have a
length that extends approximately the width of the thermal
processing chamber. The linear lamps 24 are placed in a parallel
configuration and are horizontally oriented with respect to a wafer
being heated. For example, referring to FIG. 5, the semiconductor
wafer 14 is shown in phantom for providing a visual comparison
between the linear lamps 24 and the diameter of the wafer.
In accordance with the present invention, in order to heat a wafer
more uniformly, heating device 22 further includes tuning devices
40 which, in this embodiment, are generally positioned in between
the linear lamps 24. Tuning devices 40 are designed to emit
controlled and focused amounts of light energy onto particular
locations of a semiconductor wafer being heated. The tuning devices
are provided in order to make fine adjustments to the irradiance
distribution produced by lamps 24 in order to more precisely heat
the wafers. For example, tuning devices 40 can be used to emit
controlled amounts of light energy between the radial heating zones
located on the wafer.
Tuning devices 40 as shown in FIGS. 2 through 4 are active
localized sources of focused light energy. The tuning devices can
be, for instance, laser diodes having a relatively high power. For
instance, the tuning source can contribute from about 1% to about
30% of the local power density irradiating the wafer at the
selected position. In an alternative embodiment, tuning devices 40
can be a lamp, such as a tungsten halogen lamp or arc lamp, in
operative association with one or more focusing lenses or
reflectors.
In FIGS. 2 through 4, tuning devices 40 include a light energy
source coupled to a light pipe or a fiberoptic 78 and a focusing
lens 80. Light pipe 78 and focusing lense 80 serve to direct the
light energy onto a particular location of the wafer. These
elements, however, may not be necessary in all applications.
Instead of or in addition to conventional laser diodes, a tunable
laser means can also be used as a laser source. The wavelength of
light emitted by the tunable laser device can be adjustable.
Consequently, the wavelength of the tuning source can be adapted or
adjusted to the texture or state of the illuminated wafer region,
which can include structures in the lateral direction and/or
structures of layers of different dielectric constants. More
particularly, the wavelength of the tuning source can be adjusted
in order to maximize absorption.
The number of tuning devices 40 that may be used in a system of the
present invention can vary depending upon the particular
application. For most applications, however, tuning devices will be
positioned so as to heat the outer edges of the wafer. As shown in
FIG. 5, many other tuning devices 40 can also be included in the
system.
During operation, heating device 22 is preferably in communication
with a system controller 50 as shown in FIG. 1. Based upon the
temperature of the wafer being heated, system controller 50 can be
designed to vary the amount of light energy being emitted by lamps
24 and by tuning devices 40.
Besides light energy intensity, other parameters of the tuning
device can be controlled as a function of the wafer temperature or
the temperature of another part of the wafer processing system.
These parameters can be controlled as a function of other
parameters relevant to the processing of wafers, like e.g. process
time, conditions of the processed gas such as temperature, pressure
or composition, or ramp rate which refers to the rate at which the
wafer is heated or cooled. Other parameters of the tuning device
that can be controlled include e.g. the emitted spectrum, pulse
parameters such as time, duty-factor or frequency, pulse-shape,
frequency-time characteristics if the device is used in a pulse
mode, the spacial position of the device relative to the wafer, the
state of polarization, the size and angle of the illuminated area
on the wafer, coherence in time and space, and parameters of any
optical devices such as apertures, filters, lenses of various kind,
mirrors which e.g. at least partly but not necessarily surround the
light source of the tuning device.
Referring to FIG. 6, one embodiment of a tuning device made in
accordance with the present invention is illustrated. In this
embodiment, like reference numerals have been used in order to
indicate similar elements as shown in the other figures. As shown,
tuning device 40 includes a light energy source 42 which transmits
light to a wafer 14 in a thermal processing chamber through a
window 32. Light energy source 42 is positioned above heating
device 22, which includes a plurality of linear lamps 24.
In this embodiment, light energy source 42 is an arc lamp that
includes a cathode spaced from an anode. During operation, the
cathode emits electrons that travel across the lamp arc gap and
strike the anode. Arc lamps typically emit ultra violet light,
infrared light, and visible light. In one embodiment, the emitted
spectrum of the arc lamps can be controlled by current density. The
current density can be controlled by power supply and adjusting the
voltage or internal resistance of the supply. The current density,
however, can also be controlled by external magnetic fields. If the
arc lamps are used in a pulsed mode, a high current density is
achievable, resulting in very intense emitted UV radiation.
The power level of the lamp can vary depending upon the particular
application. Power levels from 125 watts to 1500 watts are
available. Each of these power levels is actually a power range,
with nominal power near the maximum. For most applications,
however, the lamp should have a power level of from about 180 watts
to about 320 watts.
As illustrated, arc lamp 42 is surrounded by a reflector 70.
Reflector 70 preferably has a pure polycrystalline alumina body
that is glazed with a high temperature material to give the
reflector a specular surface. For instance, the reflector can be
coated with a silver alloy for a visible lamp or an aluminum
coating for a UV lamp and/or dielectric coating.
Reflector 70 surrounds the light energy source and can have various
shapes. For instance, reflector 70 can be parabolic or elliptical.
A parabolic reflector will create a collimated output beam, while
an elliptical reflector will create a focused output. For most
applications, preferably an elliptical reflector is used, because
of its slightly better collection efficiencies and slightly shorter
arc gap, while parabolic reflectors are usually used with focusing
lenses.
During operation, preferably arc lamp 42 is cooled. For example the
lamp can be cooled using forced air, free convention, conduction,
or can be water cooled.
The cathode assembly and the anode assembly of arc lamp 42 are
sealed within the reflector by a lamp window 72. Lamp window 72 can
be made from, for instance, a ground and polished single-crystal
sapphire.
As shown in the Figure, light emitted by arc lamp 42 is directed
through a pair of apertures or "stops" 74 and 76 to block stray
light. The reflector 70 focuses the light energy into a light pipe
78. One or more lenses are then used to focus the light out of the
pipe and onto the wafer surface. Light pipe 78 is preferably made
from a material that is well adapted for transmitting light and
that is not substantially thermally conductive, such as quartz.
From light pipe 78, the light is passed through several focusing
lenses prior contacting a semi-conductor wafer 14. For instance, as
shown in the embodiment illustrated in FIG. 6, the system includes
a first focusing lens 80, a second focusing lens 82, and a third
focusing lens 84. Focusing lens 84 is positioned on the opposite
side of window 32 within the thermal processing chamber in which
the wafer is held. Focusing lenses 80, 82 and 84 are designed to
facilitate transmission of light energy being emitted by arc lamp
42 and to focus the light onto a particular location of the wafer.
In this embodiment, focusing lenses 80 and 82 comprise a condensing
lens set. It should be understood, however, that the number and
combination of lenses can vary depending on the application. For
instance, the number of lenses can be reduced with careful lens
design, such as by using an aspherical lens. Alternatively or in
combination also Fresnel-Zone-Plates or other refractive and/or
diffractive means and/or reflective optics (e.g. an elliptical
reflector) can be used to get the desired illumination on the
wafer.
Tuning device 40 as shown in FIG. 6 can be used to heat various
locations of the wafer. In one embodiment, however, it has been
found that this configuration is particularly well adapted to
heating the outer edges of the wafer, where the wafer tends to lose
heat due to radiation and convection during heating cycles. In
particular, it has been found that the system illustrated in FIG. 6
is particularly well adapted to heating the outer 3 to 5
millimeters of the wafer. It should be understood, however, that
tuning device 40 can be positioned to heat other locations on the
wafer.
The configuration illustrated in FIG. 6 represents one embodiment
of a single tuning device using an arc lamp. It should be
understood that more than one tuning device may be used in a single
system. Further, the location of the tuning device can vary. For
instance, in an alternative embodiment, the tuning device can be
below or on the side of the heater. Further, in one embodiment,
wafer 14 can be heated from the top and the bottom with the tuning
devices. For example, the wafer can be heated from the bottom using
a separate heating device containing various tuning devices.
Further, the tuning device can be arranged in a linear position
with respect to the wafer or can assume an angular position with
respect to the wafer.
Besides arc lamps as shown in FIG. 6, the tuning device of the
present invention can also be a laser. Lasers can be used alone or
in combination with arc lamps.
In general, lasers emit light at a particular wavelength. Because
lasers emit a narrow spectral band of radiation, however, it may be
beneficial in some applications to couple the light emission from
the laser with the absorption properties of the wafer being heated.
For instance, a wafer can be coated with a material or a thin-film
stack that may be highly reflective at the wavelength at which the
laser operates, which reduces the efficiency at which the wafer is
heated by the laser. In accordance with the present invention,
however, various techniques can be used to increase absorption
efficiencies when using lasers.
For example, in one embodiment, several different types of lasers
can be used in the heating device that each emit light at different
wavelengths. Thus, when a particular substrate is highly reflective
at the wavelength at which one laser operates, a second laser
operating at a different wavelength can be used to heat the wafer.
The radiation from the different lasers may be optically combined
before contacting the wafer. Alternatively, several beams of light
from the different lasers could illuminate a selected area of the
wafer. In still another alternative embodiment, several beams of
light could irradiate the same wafer radius as the wafer is
rotated.
In addition to using multiple lasers at different wavelengths, the
position of each laser can be arranged so as to maximize
absorption. More specifically, absorption can be maximized by
adjusting the plane of polarization and the angle of incidence of
light being emitted by the laser with respect to the surface of the
wafer.
For instance, the reflectivity of most surfaces is a function of
the angle of incidence. Thus, changing the angle of incidence of
the laser light contacting the wafer can increase absorption. In
this embodiment, the laser sources can all be angled so as to
maximize absorption for a particular wafer. Alternatively, the
angle of incidence of each laser source can be different so as to
ensure that at least one of the tuning sources will have a high
degree of absorption during the heating process. The angle of
incidence can also be a parameter which is controlled by the system
controller 50 as a function of another parameter in the system,
such as those mentioned above.
For most applications, when adjusting the angle of incidence, the
laser beams of light should be placed in the p-polarization plane
with respect to the wafer surface. The p-polarization plane is
where in the electric field vector of the incident radiation lies
in the plane of incidence. The plane of incidence is the plane
containing the incident beam and the normal to the wafer surface.
For light with this polarization, the reflectivity of many
materials, including silicon, can become small for angles of
incidence of less than 90.degree.. In particular, reflectivity,
which can be a function of temperature, is very low such as almost
zero near a critical angle i.e. the Brewster angle. For silicon,
the Brewster angle is approximately 75.degree.. Since laser beams
are often inherently polarized, altering the angle of incidence
when using lasers can be particularly effective in accordance with
the present invention.
For example, in one embodiment, when using a laser, the angle of
incidence can be from about 40.degree. to about 85.degree. and
particularly from about 60.degree. to about 85.degree. when heating
a silicon wafer.
In general, any suitable type of laser can be used in the present
invention. In one embodiment, a laser diode is used. Laser diodes
efficiently convert electricity into laser radiation and are
available in high power ratings. For example, high power devices,
delivering continuous power of greater than 10 watts are currently
commercially available, with emission wavelengths between 400 nm
and 4000 nm. The above described lasers can be combined with beam
delivery optics that reshape the emitted beam and direct it to the
wafer. For example, the laser can be coupled with fiber optics for
guiding the light onto a particular location of the wafer.
In an alternative embodiment, or in combination with the above
embodiments, the tuning device can include a plurality of light
pipes, such as optical fibers. The light energy of the tuning
device can be distributed with the light pipes to at least two
local areas within the chamber and/or the wafer. Preferably, the
local areas are separated from each other and are illuminated by
the same tuning device. The areas, however, can overlap or can be
essentially identical, meaning that the two light pipes illuminate
the same area. This tuning device configuration can be used for
illuminating the wafer at the same region from the top and the
bottom using a single tuning device, such as having e.g. the same
spectral conditions for the top and the bottom illumination.
When using a plurality of light pipes for a single tuning device,
the tuning device can also include a system of apertures or
aperture plates having a predetermined pattern of apertures. In
this embodiment, certain light pipes can be selected from the
plurality of light pipes. For example, a laser, arc lamp or halogen
lamp can be placed in communication with a plurality of light
pipes. One of the light pipes can then be selected for transferring
the light energy to the wafer. The particular light pipes selected
can control the intensity of the energy transported through the
pipe, having the advantage that no power control of the light
source itself is necessary. Such a control can be difficult for
certain lasers (e.g. super radiating systems like a spark pumped
nitrogen laser) or arc lamps (e.g. in pulsed mode with very high
current density).
Alternatively, instead of using a plurality of light pipes in
conjunction with the above-mentioned apertures, the intensity of
the light emitted from the tuning source can be controlled using
polarization filters. Further, there is also the possibility of
simply turning the tuning devices on and off independent of the
primary heating lamps for controlling the irradiance
distribution.
So as mentioned, the electomagnetic power of the tuning devices can
be delivered to the specified regions of the wafer from either
above or below the wafer, or from both sides. The latter case gives
the advantage of reducing the possibility that there is poor power
coupling because of the presence of a reflective coating on one
side of the wafer. This concept can be applied equally well to the
arc lamps or the laser sources, and it can be implemented by either
having separate sources built into the chamber above and below the
wafer, or through the use of light pipes as described above e.g.
fibers that transmit the energy from the tuning device in these
locations. The tuning devices could also irradiate the wafer edge
from the side. This is especially useful in cases where a slip-free
ring (i.e. a heating ring used to heat the edges of a wafer) is not
present in the system. Light sources to be built into the side of
the chamber, which would not interfere with the mechanical layout
of the linear lamp rays so much, also can be used as tuning
devices. Irradiation from the side can fall directly on the edge of
the wafer, but it is also possible for the illumination to cause
light to fall on the top and bottom surfaces of the wafer over a
region close to the edge. This light can be incident at a rather
large angle of incidence, and in this configuration it is quite
convenient to achieve angles of incidence close to the critical
angle for silicone (approximately 75.degree. to the normal), where
power coupling is strong, and coating effects could be
minimized.
These and other modifications and variations to the present
invention may be practiced by those of ordinary skill in the art,
without departing from the spirit and scope of the present
invention, which is more particularly set forth in the appended
claims. In addition, it should be understood that aspects of the
various embodiments may be interchanged both in whole or in part.
Furthermore, those of ordinary skill in the art will appreciate
that the foregoing description is by way of example only, and is
not intended to limit the invention so further described in such
appended claims.
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